git-commit-vandalism/Documentation/object-format-disclaimer.txt

THIS OPTION IS EXPERIMENTAL! SHA-256 support is experimental and still
in an early stage.  A SHA-256 repository will in general not be able to
share work with "regular" SHA-1 repositories.  It should be assumed
that, e.g., Git internal file formats in relation to SHA-256
repositories may change in backwards-incompatible ways.  Only use
`--object-format=sha256` for testing purposes.
Documentation: mark `--object-format=sha256` as experimental After eff45daab8 ("repository: enable SHA-256 support by default", 2020-07-29), vanilla builds of Git enable the user to run, e.g., git init --object-format=sha256 and hack away. This can be a good way to gain experience with the SHA-256 world, e.g., to find bugs that GIT_TEST_DEFAULT_HASH=sha256 make test doesn't spot. But it really is a separate world: Such SHA-256 repos will live entirely separate from the (by now fairly large) set of SHA-1 repos. Interacting across the border is possible in principle, e.g., through "diff + apply" (or "format-patch + am"), but even that has its limitations: Applying a SHA-256 diff in a SHA-1 repo works in the simple case, but if you need to resort to `-3`, you're out of luck. Similarly, "push + pull" should work, but you really will be operating mostly offset from the rest of the world. That might be ok by the time you initialize your repository, and it might be ok for several months after that, but there might come a day when you're starting to regret your use of `git init --object-format=sha256` and have dug yourself into a fairly deep hole. There are currently topics in flight to document our data formats and protocols regarding SHA-256 and in some cases (midx and commit-graph), we're considering adjusting how the file formats indicate which object format to use. Wherever `--object-format` is mentioned in our documentation, let's make it clear that using it with "sha256" is experimental. If we later need to explain why we can't handle data we generated back in 2020, we can always point to this paragraph we're adding here. By "include::"-ing a small blurb, we should be able to be consistent throughout the documentation and can eventually gradually tone down the severity of this text. One day, we might even use it to start phasing out `--object-format=sha1`, but let's not get ahead of ourselves... There's also `extensions.objectFormat`, but it's only mentioned three times. Twice where we're adding this new disclaimer and in the third spot we already have a "do not edit" warning. From there, interested readers should eventually find this new one that we're adding here. Because `GIT_DEFAULT_HASH` provides another entry point to this functionality, document the experimental nature of it too. Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com> 2020-08-16 12:01:18 +02:00			`THIS OPTION IS EXPERIMENTAL! SHA-256 support is experimental and still`
			`in an early stage. A SHA-256 repository will in general not be able to`
			`share work with "regular" SHA-1 repositories. It should be assumed`
			`that, e.g., Git internal file formats in relation to SHA-256`
			`repositories may change in backwards-incompatible ways. Only use`
			`--object-format=sha256` for testing purposes.